Thermoplastic vulcanizates include blends of dynamically cured rubber and thermoplastic polymers. The rubber may be dispersed within the thermoplastic resin phase as finely-divided rubber particles. These compositions have advantageously demonstrated many of the properties of thermoset elastomers, yet they are processable as thermoplastics.
The ability to adhere these compositions to polar surfaces, however, has presented technological challenges. U.S. Pat. No. 4,957,968 teaches thermoplastic vulcanizates that include a functionalized polyolefin. For example, these thermoplastic vulcanizates may include polypropylene grafted with maleic anhydride. These thermoplastic vulcanizates, which may be partially or completely crosslinked, demonstrate useful adhesion to metal surfaces.
U.S. Pat. No. 6,503,984 teaches thermoplastic vulcanizates that exhibit improved adhesion to polar polymers and metals. These thermoplastic vulcanizates include a first polyolefin that is characterized by a low crystallinity (e.g., 10-32 weight percent) and low flexural modulus (e.g., 34.5-138 MPa), and a second polyolefin including a functionalized polyolefin (e.g., maleated polypropylene). The first polyolefin may include homopolymers with low crystallinity due to random or regular variations in tacticity, copolymers that have low crystallinity due to comonomer and/or random or regular variations in tacticity (including blocky homo and copolymers), and polymers prepared by blending or grafting together oligomers or polymers.
Inasmuch as there is continued demand for thermoplastic vulcanizates that exhibit technologically useful adherence to polar surfaces, there remains a need to improve upon these compositions.